Douglas Isbell
Headquarters, Washington, DC December 30, 1998
(Phone: 202/358-1753)
Helen Worth
Johns Hopkins University Applied Physics Laboratory, Laurel, MD
(Phone: 240/228-5113)
RELEASE: 98-228
NEAR SPACECRAFT SET FOR JAN. 3 BURN
A confident NEAR mission operations team is preparing to
fire the main engine of the Near Earth Asteroid Rendezvous
(NEAR) spacecraft at noon on Jan. 3 to put the mission on
course for a rendezvous with its target, asteroid 433 Eros, in
just over a year.
The upcoming burn will last 24 minutes and will increase
the spacecraft's speed by 2,100 mph (939 meters per second),
putting it at close to the same speed as Eros. The burn will
be divided into an initial three-minute "settling burn" with
the spacecraft's small hydrazine thrusters that will change its
velocity by only 11 mph (five meters per second), and a 21-
minute firing of the bipropellant main engine that will provide
the rest of the velocity change.
The burn will lessen the distance between NEAR and Eros as
they orbit the sun. For the next year NEAR will travel behind
Eros in a slightly closer orbit to the sun. By mid-February
2000, NEAR will catch up to Eros. The spacecraft will then
enter orbit around Eros and begin its planned yearlong study of
the asteroid.
The spacecraft's first attempted rendezvous burn was
aborted on Dec. 20, 1998, just seconds after the settling burn
was completed. An investigation by mission personnel revealed
that the brief engine burn exceeded certain safety limits
associated with the onboard system that autonomously controls
the spacecraft. This resulted in the engine abort.
Reprogramming of these values is now being completed and the
spacecraft will be ready for the Jan. 3 burn.
"We're very confident that we've found the problems
associated with the Dec. 20 abort," says Thomas B. Coughlin,
NEAR Project Manager at the Johns Hopkins University Applied
Physics Laboratory (APL) in Laurel, MD, which manages the
mission for NASA. "The abort lost us time but the flyby gave
us valuable information about Eros' shape and mass that we
wouldn't have had -- information that will help us during our
orbital phase a little more than a year from now."
Because the spacecraft did not complete the Dec. 20 burn,
the opportunity to orbit Eros next month as originally planned
was lost. The setback presented mission planners with a huge
challenge but also an unexpected opportunity. Within days of
the abort, the NEAR team developed a complicated command
sequence for a Dec. 23 flyby of Eros to obtain multicolor
images, near-infrared spectra, and magnetic field measurements.
The commands were uploaded swiftly to the spacecraft and
executed as planned, producing images of the asteroid and
valuable data that is now being processed.
Despite the delay, NEAR is expected to complete all its
science objectives. To follow the NEAR mission as it unfolds,
visit the project Web site at: http://near.jhuapl.edu
Updates on mission activities and science results are also
available by phone on the NEAR Hot Line at (240) 228-5413. Due
to the rescheduling of mission events, the previously announced
Jan. 10 and Jan. 14 press briefings have been canceled.